The present invention relates to a control for a structural assembly oscillatingly supported around a swivel axis on a base unit in a harvesting machine.
In the following specification, the invention is described with reference to a cutter table oscillatingly secured to a harvester thresher as representing all such structural assemblies as mowers, harvesters and other harvesting machines.
In the operation of a harvester thresher, the cutter of this machine, in the majority of cases, has to be so guided over the ground that it will not dig into the soil but on the other hand will support its residual weight on the ground so as not to lift up in case of ground unevennesses but rather will follow these unevennesses of the ground and cut the wheat at a constant height.
In order to determine the residual weight, the cutter tables are supported by springs relative to the undercarriage.
In the past, the cutter table used to be mostly secured rigidly to the conveyor channel and thus in parallel to the transversal axis of the harvester thresher. For lifting or lowering, respectively, the cutter table, the cutter table was rotated around its transversal axis.
In the operation, for instance in an inclined field, if very broad cutter tables are used it might happen that the table digs into the ground at the lower side of the field inclination since the heavy harvester thresher will, with its wheels, sink deeper into the ground at the lower side of the inclination then on the upper side. The machine with its transversal axis is not, therefore, in parallel to the inclination of the ground. The cutter table which is often twice as wide as the machine, unless it can slue or swing around the longitudinal axis of the harvester thresher, does not have an inclination parallel to the ground. On the lower side of the inclined field, it will dig into the ground and on the upper side of the field it will be guided at a distance above ground.
Inclination equalizing systems are on the market which adjust the inclination of the cutter table. These systems are designed as freely swinging or oscillating systems wherein the cutter table is kept in the optimum inclination by the ground contact pressure or is kept in position by force-actuated swiveling devices.
Such devices may directly be mounted at the conveyor channel and the cutter table, but they may also constitute part of a two-piece adapter one part of which is assigned to the conveyor channel and the second to the cutter table. The oscillating systems operate in a way that one adapter part can be swung relative to the second adapter part. Such an adapter oscillation system has the advantage that neither the conveyor channel nor the cutter table originally provided without an oscillation system have to be changed.
The free oscillation of the cutter table has the advantage that the ground contact of the cutter table determines its optimum inclination. Such systems have for instance been known from German Offenlegungsschrift No. 35 44 918 and GDR Patent Specification No. 94,725. Free oscillation is the more functional the easier the table can oscillate.
The majority of cutter tables, however, have so been designed that they are imbalanced relative to the centre of the latitude since the weight of the drives for cutter knives, drawing-in worm gear and winch have mostly been provided on only one cutter table side. In case of a free oscillation around a central axis, the cutter table is therefore inclined to the heavier side. The operation of the free oscillation is seriously hampered.
In order to balance out the equilibrium, additional weights have been mounted on the lighter side; it is not, however, of advantage to additionally increase the weight of the cutter table which is heavy by itself.
In order to provide for equilibrium in case of an imbalanced cutter table, a spring mechanism has been described, according to German Offenlegungsschrift No. 35 44 918, wherein via an angular lever a roller support is provided on the bracket of the conveyor channel, the roller support being spring-loaded.
This sophisticated structure is very much endangered through damages when affixing the cutter table and, secondly, it has to be correspondingly biased at each coupling process in order to have the spring force available over the whole oscillation range.
A similar mode of operation has been described in German Patent Specification No. 2,208,243. But in this case, too, the great disadvantage consists in that when coupling the cutter table on or off, the equalizer spring either has to bias, or relax, respectively, itself or has to be manually released prior to coupling off or manually tensioned after coupling on. If the spring tensions or relaxes automatically in the coupling process, the danger of an accident is imminent since the cutter table wants to position itself about half the oscillation path in oblique position relative to the conveyor channel before it is completely coupled on or off. This effect arises because the spring with a view to the path-dependent changing spring force does not operate evenly over the whole oscillation path.
When the cutter table is lifted, it is important and desirable that the cutter table oscillates into its position parallel to the harvester thresher. Particularly with a view to the desired easy-moving free oscillation, the problem is encountered that unless corresponding means are provided which lock oscillation as soon as the table is lifted, the cutter table will bend to and fro. This can already set in by vibrations of the machine caused by uneven ground but also by uneven feeding of the table with harvested material.
In GDR Patent Specification No. 94,725 and German Patent Specifications No. 2,133,746 and 2,208,243, stabilizer springs have been described which will draw or push an oscillatingly inclined cutter table into the parallel again as soon as the table is taken from ground contact. These springs however have beforehand to be biased during the oscillation process and hence impair the smoothness of the oscillation movement when copying the ground contour. The ground contact pressure required for guiding the table according to the ground contour must for this reason be selected higher and the disadvantages thereof have to be accepted.
Controlled oscillation is provided by one or two hydraulic cylinders. This can be performed by manually operated control of the hydraulic cylinders or by sensors on the cutter table trough which scan the distance of the cutter table from the ground and pass corresponding pulses to the control valve for the hydraulic cylinders. The problem in case of manual control is that, particularly in case of bad view caused by dust or darkness, the table inclination is not exactly seen by the operator. This causes in many cases that a highly uneven stubble height corresponding to the width of the cutter table is obtained. This again is of disadvantage for subsequent stubble processing.
Sensors, scanners and similar devices ascertaining the ground contour have the great disadvantage that they have to be provided too far behind the cutter edge and therefore can actively react only when the cutter bar has already passed the changed ground contour and, secondly, cannot differentiate genuine from non-genuine obstacles. A heap of straw or loose soil should not initiate action whereas for instance a heavy stone should provide that the cutter table is actively oscillated.
The free oscillation according to the ground contour by the weight of the cutter table supported on the ground, as referred to, is to be preferred when guiding automatically. In this case, the two outer skids which as a rule extend beyond the cutter edge of the cutter table are sufficient to generate, by their supporting force on the ground, the oscillating movement of the cutter table. On the other hand, however, it is also desirable to be able to manually adjust the inclination in case of a higher-adjusted cutter table.
In both cases, however, the cutter table should automatically find its position in parallel to the transversal axis of the harvester thresher if the operator so wishes.